Personal computers are being equipped more and more frequently with modems, enabling them to communicate with remote computers via the telephone network.
Simultaneously, portable computers are being used more and more, and they have the specific purpose of travelling with their users and thus of being used in different countries.
However, in most countries, any device, such as a modem, for connection to the public telephone network of the country, must be specifically approved ("PTT approved"), which approval is obtained by a special approval procedure, and has the purpose of ensuring that certain electrical characteristics of the device are suitable for operating on the network. These electrical characteristics vary from one country to another.
Thus, to be able to use a portable computer with its modem in different countries, it is necessary at present to possess a plurality of interchangeable modem cards, each approved for a specific country. This procedure is naturally expensive and bulky, thereby causing a portable computer to lose much of its theoretical advantage, in practice.
To mitigate this drawback, proposals have already been made in the prior art to provide a modem fitted with a modulator/demodulator circuit associated with a computer interface circuit, which circuits are common for all countries, and a telephone line interface circuit which varies depending on the country of use. Thus, a portable computer user who desires to be able to connect the computer to the public telephone networks of different countries merely needs to possess a single main modem card which is permanently installed in the computer, together with a plurality of telephone line interfaces. Such modems are described in FR-A-2 652 173 and EP-A-0 309 627.
However, the above-mentioned drawbacks are not eliminated, they are merely reduced. The user still needs to possess a plurality of different telephone line interface boxes, and must swap them over as necessary each time the computer is to be connected to the public telephone network of a new country.
The present invention seeks to eliminate the said drawbacks and to provide a modem for which the circuitry is identical for all countries, with hardware matching being performed for use in different countries without physically removing or adding components, and in a manner that is transparent to the user.